Hydroxyl groups on cellulose nanocrystal surfaces form nucleation points for silver nanoparticles of varying shapes and sizes

Dafne Musino,Camille Rivard,Gautier Landrot,Bruno Novales,Thierry Rabilloud,Isabelle Capron

doi:10.1016/j.jcis.2020.09.082

Abstract

In this study, we investigate the interactions between the cellulose surface and Ag nanoparticles (AgNPs) for the purpose of manufacturing hybrid nanomaterials using bacterial cellulose nanocrystals (BCNs) as a model substrate. We focus on the role of the BCN surface chemistry on the AgNP nucleation obtained by chemical reduction of Ag+ ions. Homogeneous hybrid suspensions of BCN/AgNP are produced, regardless of whether the BCNs are quasi-neutral, negatively (TBCNs) or positively charged (ABCNs). The characterization of BCN/AgNP hybrids identifies the –OH surface groups as nucleation points for AgNPs, of about 20 nm revealing that surface charges only improve the accessibility to OH groups. X-ray Absorption technics (XANES and EXAFS) revealed a high metallic Ag0 content ranging from 88% to 97%. Moreover, the grafting of hydrophobic molecules on a BCN surface (HBCNs) does not prevent AgNP nucleation, illustrating the versatility of our method and the possibility to obtain bifunctional NPs. A H2O2 redox post-treatment on the hybrid induces an increase in AgNPs size, up to 90 nm as well as a shape variation (i.e., triangular). In contrast, H2O2 induces no size/shape variation for aggregated hybrids, emphasizing that the accessibility to –OH groups ensures the nucleation of bigger Ag nano-objects.

Highlights

Cellulose is an almost inexhaustible biopolymer extracted from wood, cotton, algae, tunicates or bacteria [1,2,3], leading to variation in dimensions and structural organization [4]
Even though the global morphology of the nanocrystals remained unchanged after modification, it could be observed that TBCNs and ABCNs were better dispersed in comparison to quasi-neutral unmodified bacterial cellulose nanocrystals (BCNs) and hydrophobic molecules on a BCN surface (HBCNs)
Working with bacterial cellulose nanocrystals (BCNs) as model substrate, we experimentally showed that the hydroxyl groups serve as nucleation points for Ag nanoparticles (AgNPs) through ion-dipole interaction and that the surface charges only promoted nanocrystal dispersion, improving accessibility to the OH groups

Summary

Introduction

Cellulose is an almost inexhaustible biopolymer extracted from wood, cotton, algae, tunicates or bacteria [1,2,3], leading to variation in dimensions and structural organization [4]. Such an adsorption is greater on cationized cellulose fibers than on untreated ones To obtain these cationized fibers, Dong et al [40] propose to graft ammonium ions onto the surface, creating two different pathways for the deposition of metal NPs (e.g., Au, Pt, Pd): the first one based on the electrostatic assembly of metal nanoparticles capped with negative citrate ions, and a second one where negative metal complex ions are adsorbed onto the cationic substrate and reduced. The size-shape transformation of AgNPs achieved with H2O2 relies to redox capabilities linked to the autocatalytic decomposition on the Ag surface These AgNPrisms are anisotropic (i.e., their lateral dimension is greater than their thickness) and are characterized by a strong localized surface plasmon resonance (LSPR). The presence of a predominant (111) peak in the XRD pattern allows them to affirm that AgNPrisms are bounded to cellulose nanofibers

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Results

Conclusion